The experimental data on incommensurate phase versus temperature, as they have been obtained by high resolution inelastic neutron scattering, are compared to theoretical models. In the experiments reported we have set out to examine the phonon dispersion surface to verify that the charge-density wave (CDW) state is present continuously at temperature even above TCDW. The position of the phonon minimum (qmin = qCDW), as well as the detailed shape of the dispersion surface of phonon modes over an extended areas in the (E, q) space, is important in view of the debate on the origin of the CDW at the Peierls transition (2nd_order phase) and gives rise to a further modulation of the structure. This work confirms that the CDW state has precursor effects before the phase transition, there is a strong coupling between phonon and electronic states and that a 'soft-mode transition' occurs at TCDW. This result is compared to theories discussing the origin of the CDW state.